New Zealand's supreme court has agreed to hear an appeal by internet entrepreneur Kim Dotcom, who is being sought by the United States for alleged copyright piracy.

Dotcom's lawyers want to view all of the evidence US authorities will use against their client in an extradition hearing scheduled for August.

They argued that withholding the evidence put Dotcom at a disadvantage in fighting the extradition case.

The district and high courts in Auckland had approved the disclosure of evidence, but this was overturned on appeal by US authorities earlier this year.

Dotcom can now appeal to the supreme court against the ruling and it will hear his appeal on July 30.

The Megaupload founder, along with six associates, is facing extradition to the US to face charges of conspiring to infringe copyright, launder money and commit racketeering and fraud.

The US began a criminal copyright case against Dotcom in January 2012, when New Zealand law enforcement officers acting on a request from Washington conducted a dramatic raid on his mansion outside Auckland.

The extradition hearing scheduled for August may be delayed due to separate cases which have emerged after a court last year found that New Zealand used unlawful warrants in his arrest and illegally spied on him in the lead-up to the raid.

The copyright case could set a precedent for internet liability laws and, depending on its outcome, may force entertainment companies to rethink their distribution methods.

Dotcom maintains that Megaupload, which housed everything from family photos to Hollywood blockbusters, was merely a storage facility for online files and should not be held accountable if content stored on the site was obtained illegally.